Hybrid time and frequency domain csi feedback scheme

Abstract

In a downlink multi-user multiple input multiple output (DL MU-MIMO) system, channel state information (CSI) feedback duration may strongly affect media access control (MAC) efficiency. While a time domain compression may give a significant reduction in feedback duration, the time domain compression may have complexity issues at the station (STA). In particular, for time domain compression, a large complex matrix multiplication may be required at the client to estimate a cyclic prefix (CP) length impulse response, which best models the frequency response of the channel. Embodiments of the invention comprise a hybrid scheme that may reduce the above complexity while maintaining significant compression gains.

1 . A method for wireless transmissions, comprising:
 estimating a multiple input multiple output (MIMO) channel used to receive transmissions from an access point (AP);   generating a truncated channel impulse response for the estimated channel;   generating frequency domain feedback for a subset of tones of the estimated channel; and   transmitting channel state information (CSI) feedback to the AP, the CSI feedback comprising the truncated channel impulse response and the frequency domain feedback.   
     
     
         2 . The method of  claim 1 , wherein the subset of tones comprises at least one of band edge tones and direct current (DC) tones. 
     
     
         3 . The method of  claim 1 , wherein generating the truncated channel impulse response comprises:
 windowing the estimated MIMO channel using the subset of tones;   taking an Inverse Fast Fourier Transform (IFFT) of the windowed MIMO channel to generate a channel impulse response; and   truncating the channel impulse response to a cyclic prefix (CP) length to generate the truncated channel impulse response.   
     
     
         4 . The method of  claim 1 , wherein transmitting comprises:
 quantizing the truncated channel impulse response and the frequency domain feedback; and   transmitting three bits of a scaling factor per tap.   
     
     
         5 . An apparatus for wireless communications, comprising:
 logic for estimating a multiple input multiple output (MIMO) channel used to receive transmissions from an access point (AP);   logic for generating a truncated channel impulse response for the estimated channel;   logic for generating frequency domain feedback for a subset of tones of the estimated channel; and   logic for transmitting channel state information (CSI) feedback to the AP, the CSI feedback comprising the truncated channel impulse response and the frequency domain feedback.   
     
     
         6 . The apparatus of  claim 5 , wherein the subset of tones comprises at least one of band edge tones and direct current (DC) tones. 
     
     
         7 . The apparatus of  claim 5 , wherein the logic for generating the truncated channel impulse response comprises:
 logic for windowing the estimated MIMO channel using the subset of tones;   logic for taking an Inverse Fast Fourier Transform (IFFT) of the windowed MIMO channel to generate a channel impulse response; and   logic for truncating the channel impulse response to a cyclic prefix (CP) length to generate the truncated channel impulse response.   
     
     
         8 . The apparatus of  claim 5 , wherein the logic for transmitting comprises:
 logic for quantizing the truncated channel impulse response and the frequency domain feedback; and   logic for transmitting three bits of a scaling factor per tap.   
     
     
         9 . An apparatus for wireless communications, comprising:
 means for estimating a multiple input multiple output (MIMO) channel used to receive transmissions from an access point (AP);   means for generating a truncated channel impulse response for the estimated channel;   means for generating frequency domain feedback for a subset of tones of the estimated channel; and   means for transmitting channel state information (CSI) feedback to the AP, the CSI feedback comprising the truncated channel impulse response and the frequency domain feedback.   
     
     
         10 . A computer-program product for wireless communications, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:
 instructions for estimating a multiple input multiple output (MIMO) channel used to receive transmissions from an access point (AP);   instructions for generating a truncated channel impulse response for the estimated channel;   instructions for generating frequency domain feedback for a subset of tones of the estimated channel; and   instructions for transmitting channel state information (CSI) feedback to the AP, the CSI feedback comprising the truncated channel impulse response and the frequency domain feedback.   
     
     
         11 . A method for wireless communications, comprising:
 receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising a truncated channel impulse response for an estimated multiple input multiple output (MIMO) channel used to transmit transmissions to the AT and frequency domain feedback for a subset of tones of the estimated channel; and   reconstructing the estimated channel based on the CSI feedback.   
     
     
         12 . The method of  claim 11 , wherein the subset of tones comprise at least one of band edge tones and direct current (DC) tones. 
     
     
         13 . The method of  claim 11 , wherein reconstructing the estimated MIMO channel comprises:
 taking a Fast Fourier Transform (FFT) of the truncated channel impulse response;   multiplying the FFT of the truncated channel impulse response with an inverse of a windowing function used at the AT to generate the truncated channel impulse response; and   replacing the subset of tones of the estimated channel with values from the frequency domain feedback.   
     
     
         14 . An apparatus for wireless communications, comprising:
 logic for receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising a truncated channel impulse response for an estimated multiple input multiple output (MIMO) channel used to transmit transmissions to the AT and frequency domain feedback for a subset of tones of the estimated channel; and   logic for reconstructing the estimated channel based on the CSI feedback.   
     
     
         15 . The apparatus of  claim 14 , wherein the subset of tones comprise at least one of band edge tones and direct current (DC) tones. 
     
     
         16 . The apparatus of  claim 14 , wherein the logic for reconstructing the estimated MIMO channel comprises:
 logic for taking a Fast Fourier Transform (FFT) of the truncated channel impulse response;   logic for multiplying the FFT of the truncated channel impulse response with an inverse of a windowing function used at the AT to generate the truncated channel impulse response; and   logic for replacing the subset of tones of the estimated channel with values from the frequency domain feedback.   
     
     
         17 . An apparatus for wireless communications, comprising:
 means for receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising a truncated channel impulse response for an estimated multiple input multiple output (MIMO) channel used to transmit transmissions to the AT and frequency domain feedback for a subset of tones of the estimated channel; and   means for reconstructing the estimated channel based on the CSI feedback.   
     
     
         18 . A computer-program product for wireless communications, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:
 instructions for receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising a truncated channel impulse response for an estimated multiple input multiple output (MIMO) channel used to transmit transmissions to the AT and frequency domain feedback for a subset of tones of the estimated channel; and   instructions for reconstructing the estimated channel based on the CSI feedback.   
     
     
         19 . A method for transmitting channel state information (CSI) feedback in 802.11 wireless communications, comprising:
 estimating a first set of frequency domain channel coefficients from very high throughput long training fields (VHT-LTFs) transmitted from an access point (AP);   generating a second set of frequency domain channel coefficients for a subset of tones;   generating the CSI feedback by quantizing the first and second sets of frequency domain channel coefficients and including additional receiver information; and   transmitting the CSI feedback to the AP.   
     
     
         20 . The method of  claim 19 , wherein estimating the first set of frequency domain channel coefficients comprises:
 generating a truncated channel impulse response; and   taking a Fast Fourier Transform (FFT) of the truncated channel impulse response to estimate the first set of frequency domain channel coefficients.   
     
     
         21 . The method of  claim 19 , wherein estimating the first set of frequency domain channel coefficients comprises:
 directly recording frequency domain channel coefficients from the VHT-LTFs.   
     
     
         22 . The method of  claim 19 , wherein the additional receiver information comprises a receiver decoder type comprising a maximum likelihood (ML) decoder and a minimum mean square error (MMSE) decoder. 
     
     
         23 . The method of  claim 20 , wherein generating the truncated channel impulse response comprises:
 windowing frequency domain channel coefficients computed from the VHT-LTFs;   taking an Inverse Fast Fourier Transform (IFFT) of the frequency domain channel coefficients using a first number of points to generate a channel impulse response; and   truncating the channel impulse response to a cyclic prefix (CP) length to generate the truncated channel impulse response.   
     
     
         24 . The method of  claim 23 , wherein the additional receiver information comprises coefficients used in the windowing function. 
     
     
         25 . The method of  claim 23 , wherein taking the FFT of the truncated channel impulse response comprises taking the FFT using a second number of points that is less than the first number of points. 
     
     
         26 . The method of  claim 21 , wherein directly recording the frequency domain channel coefficients comprises:
 directly recording from evenly spaced frequency domain tones and tones adjacent to guard tones and direct current (DC) tones.   
     
     
         27 . The method of  claim 26 , wherein the evenly spaced tones comprises tones spaced by two, three, or four tones. 
     
     
         28 . The method of  claim 19 , wherein quantizing the first and second sets of frequency domain channel coefficients comprises:
 generating three bits of a scaling factor per channel tap.   
     
     
         29 . The method of  claim 19 , wherein the subset of tones comprises at least one of band edge tones and direct current (DC) tones. 
     
     
         30 . An apparatus for transmitting channel state information (CSI) feedback in 802.11 wireless communications, comprising:
 logic for estimating a first set of frequency domain channel coefficients from very high throughput long training fields (VHT-LTFs) transmitted from an access point (AP);   logic for generating a second set of frequency domain channel coefficients for a subset of tones;   logic for generating the CSI feedback by quantizing the first and second sets of frequency domain channel coefficients and including additional receiver information; and   logic for transmitting the CSI feedback to the AP.   
     
     
         31 . The apparatus of  claim 30 , wherein the logic for estimating the first set of frequency domain channel coefficients comprises:
 logic for generating a truncated channel impulse response; and   logic for taking a Fast Fourier Transform (FFT) of the truncated channel impulse response to estimate the first set of frequency domain channel coefficients.   
     
     
         32 . The apparatus of  claim 30 , wherein the logic for estimating the first set of frequency domain channel coefficients comprises:
 logic for directly recording frequency domain channel coefficients from the VHT-LTFs.   
     
     
         33 . The apparatus of  claim 30 , wherein the additional receiver information comprises a receiver decoder type comprising a maximum likelihood (ML) decoder and a minimum mean square error (MMSE) decoder. 
     
     
         34 . The apparatus of  claim 31 , wherein the logic for generating the truncated channel impulse response comprises:
 logic for windowing frequency domain channel coefficients computed from the VHT-LTFs;   logic for taking an Inverse Fast Fourier Transform (IFFT) of the frequency domain channel coefficients using a first number of points to generate a channel impulse response; and   logic for truncating the channel impulse response to a cyclic prefix (CP) length to generate the truncated channel impulse response.   
     
     
         35 . The apparatus of  claim 34 , wherein the additional receiver information comprises coefficients used in the windowing function. 
     
     
         36 . The apparatus of  claim 34 , wherein the logic for taking the FFT of the truncated channel impulse response comprises logic for taking the FFT using a second number of points that is less than the first number of points. 
     
     
         37 . The apparatus of  claim 32 , wherein the logic for directly recording the frequency domain channel coefficients comprises:
 logic for directly recording from evenly spaced frequency domain tones and tones adjacent to guard tones and direct current (DC) tones.   
     
     
         38 . The apparatus of  claim 37 , wherein the evenly spaced tones comprises tones spaced by two, three, or four tones. 
     
     
         39 . The apparatus of  claim 30 , wherein the logic for quantizing the first and second sets of frequency domain channel coefficients comprises:
 logic for generating three bits of a scaling factor per channel tap.   
     
     
         40 . The apparatus of  claim 30 , wherein the subset of tones comprises at least one of band edge tones and direct current (DC) tones. 
     
     
         41 . An apparatus for transmitting channel state information (CSI) feedback in 802.11 wireless communications, comprising:
 means for estimating a first set of frequency domain channel coefficients from very high throughput long training fields (VHT-LTFs) transmitted from an access point (AP);   means for generating a second set of frequency domain channel coefficients for a subset of tones;   means for generating the CSI feedback by quantizing the first and second sets of frequency domain channel coefficients and including additional receiver information; and   means for transmitting the CSI feedback to the AP.   
     
     
         42 . A computer-program product for transmitting channel state information (CSI) feedback in 802.11 wireless communications, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:
 instructions for estimating a first set of frequency domain channel coefficients from very high throughput long training fields (VHT-LTFs) transmitted from an access point (AP);   instructions for generating a second set of frequency domain channel coefficients for a subset of tones;   instructions for generating the CSI feedback by quantizing the first and second sets of frequency domain channel coefficients and including additional receiver information; and   instructions for transmitting the CSI feedback to the AP.   
     
     
         43 . A method for wireless communications, comprising:
 estimating a multiple input multiple output (MIMO) channel used to receive transmissions from an access point (AP);   estimating a first set of frequency domain channel coefficients for the estimated channel from fields transmitted from the AP;   generating a second set of frequency domain channel coefficients for a subset of tones of the estimated channel;   generating channel state information (CSI) feedback by quantizing the first and second sets of frequency domain channel coefficients; and   transmitting the CSI feedback to the AP.   
     
     
         44 . The method of  claim 43 , wherein the fields transmitted from the AP comprise very high throughput long training fields (VHT-LTFs). 
     
     
         45 . The method of  claim 43 , wherein generating the CSI feedback comprises including receiver information. 
     
     
         46 . The method of  claim 45 , wherein the receiver information comprises:
 a receiver decoder type comprising a maximum likelihood (ML) decoder and a minimum mean square error (MMSE) decoder; and   window coefficients used to generate the quantized values of the first set of frequency domain channel coefficients.   
     
     
         47 . An apparatus for wireless communications, comprising:
 logic for estimating a multiple input multiple output (MIMO) channel used to receive transmissions from an access point (AP);   logic for estimating a first set of frequency domain channel coefficients for the estimated channel from fields transmitted from the AP;   logic for generating a second set of frequency domain channel coefficients for a subset of tones of the estimated channel;   logic for generating channel state information (CSI) feedback by quantizing the first and second sets of frequency domain channel coefficients; and   logic for transmitting the CSI feedback to the AP.   
     
     
         48 . The apparatus of  claim 47 , wherein the fields transmitted from the AP comprise very high throughput long training fields (VHT-LTFs). 
     
     
         49 . The apparatus of  claim 47 , wherein the logic for generating the CSI feedback comprises logic for including receiver information. 
     
     
         50 . The apparatus of  claim 49 , wherein the receiver information comprises:
 a receiver decoder type comprising a maximum likelihood (ML) decoder and a minimum mean square error (MMSE) decoder; and   window coefficients used to generate the quantized values of the first set of frequency domain channel coefficients.   
     
     
         51 . An apparatus for wireless communications, comprising:
 means for estimating a multiple input multiple output (MIMO) channel used to receive transmissions from an access point (AP);   means for estimating a first set of frequency domain channel coefficients for the estimated channel from fields transmitted from the AP;   means for generating a second set of frequency domain channel coefficients for a subset of tones of the estimated channel;   means for generating channel state information (CSI) feedback by quantizing the first and second sets of frequency domain channel coefficients; and   means for transmitting the CSI feedback to the AP.   
     
     
         52 . A computer-program product for wireless communications, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:
 instructions for estimating a multiple input multiple output (MIMO) channel used to receive transmissions from an access point (AP);   instructions for estimating a first set of frequency domain channel coefficients for the estimated channel from fields transmitted from the AP;   instructions for generating a second set of frequency domain channel coefficients for a subset of tones of the estimated channel;   instructions for generating channel state information (CSI) feedback by quantizing the first and second sets of frequency domain channel coefficients; and   instructions for transmitting the CSI feedback to the AP.   
     
     
         53 . A method for wireless communications, comprising:
 receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising:
 receiver information; 
 quantized values of a first set of frequency domain channel coefficients from very high throughput long training fields (VHT-LTFs) used to transmit transmissions to the AT; and 
 quantized values of a second set of frequency domain channel coefficients for a subset of tones; and 
   reconstructing an estimated multiple input multiple output (MIMO) channel based on the CSI feedback.   
     
     
         54 . The method of  claim 53 , wherein the subset of tones comprise at least one of band edge tones and direct current (DC) tones. 
     
     
         55 . The method of  claim 53 , wherein the receiver information comprises:
 a receiver decoder type comprising a maximum likelihood (ML) decoder and a minimum mean square error (MMSE) decoder; and   window coefficients used to generate the quantized values of the first set of frequency domain channel coefficients.   
     
     
         56 . The method of  claim 53 , wherein reconstructing the estimated MIMO channel comprises:
 taking an Inverse Fast Fourier Transform (IFFT) of the quantized values of the first set of frequency domain channel coefficients using a first number of points to generate a channel impulse response;   truncating the channel impulse response to a cyclic prefix (CP) length to generate the truncated channel impulse response;   taking a Fast Fourier Transform (FFT) of the truncated channel impulse response using a second number of points that is greater than the first number of points;   multiplying the FFT of the truncated channel impulse response with an inverse of a windowing function used at the AT to generate the truncated channel impulse response; and   replacing the subset of tones of the estimated channel with values from the quantized values of the second set of frequency domain channel coefficients.   
     
     
         57 . The method of  claim 53 , wherein reconstructing the estimated MIMO channel comprises:
 linearly interpolating the quantized values of the first set of frequency domain channel coefficients; and   replacing the subset of tones of the estimated channel with values from the quantized values of the second set of frequency domain channel coefficients.   
     
     
         58 . The method of  claim 53 , further comprising:
 computing precoder matrices using the quantized values of the first and second sets of frequency domain channel coefficients; and   linearly interpolating the precoder matrices.   
     
     
         59 . An apparatus for wireless communications, comprising:
 logic for receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising:
 receiver information; 
 quantized values of a first set of frequency domain channel coefficients from very high throughput long training fields (VHT-LTFs) used to transmit transmissions to the AT; and 
 quantized values of a second set of frequency domain channel coefficients for a subset of tones; and 
   logic for reconstructing an estimated multiple input multiple output (MIMO) channel based on the CSI feedback.   
     
     
         60 . The apparatus of  claim 59 , wherein the subset of tones comprise at least one of band edge tones and direct current (DC) tones. 
     
     
         61 . The apparatus of  claim 59 , wherein the receiver information comprises:
 a receiver decoder type comprising a maximum likelihood (ML) decoder and a minimum mean square error (MMSE) decoder; and   window coefficients used to generate the quantized values of the first set of frequency domain channel coefficients.   
     
     
         62 . The apparatus of  claim 59 , wherein the logic for reconstructing the estimated MIMO channel comprises:
 logic for taking an Inverse Fast Fourier Transform (IFFT) of the quantized values of the first set of frequency domain channel coefficients using a first number of points to generate a channel impulse response;   logic for truncating the channel impulse response to a cyclic prefix (CP) length to generate the truncated channel impulse response;   logic for taking a Fast Fourier Transform (FFT) of the truncated channel impulse response using a second number of points that is greater than the first number of points;   logic for multiplying the FFT of the truncated channel impulse response with an inverse of a windowing function used at the AT to generate the truncated channel impulse response; and   logic for replacing the subset of tones of the estimated channel with values from the quantized values of the second set of frequency domain channel coefficients.   
     
     
         63 . The apparatus of  claim 59 , wherein the logic for reconstructing the estimated MIMO channel comprises:
 logic for linearly interpolating the quantized values of the first set of frequency domain channel coefficients; and   logic for replacing the subset of tones of the estimated channel with values from the quantized values of the second set of frequency domain channel coefficients.   
     
     
         64 . The apparatus of  claim 59 , further comprising:
 logic for computing precoder matrices using the quantized values of the first and second sets of frequency domain channel coefficients; and   logic for linearly interpolating the precoder matrices.   
     
     
         65 . An apparatus for wireless communications, comprising:
 means for receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising:
 receiver information; 
 quantized values of a first set of frequency domain channel coefficients from very high throughput long training fields (VHT-LTFs) used to transmit transmissions to the AT; and 
 quantized values of a second set of frequency domain channel coefficients for a subset of tones; and 
   means for reconstructing an estimated multiple input multiple output (MIMO) channel based on the CSI feedback.   
     
     
         66 . A computer-program product for wireless communications, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:
 instructions for receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising:
 receiver information; 
 quantized values of a first set of frequency domain channel coefficients from very high throughput long training fields (VHT-LTFs) used to transmit transmissions to the AT; and 
 quantized values of a second set of frequency domain channel coefficients for a subset of tones; and 
   instructions for reconstructing an estimated multiple input multiple output (MIMO) channel based on the CSI feedback.   
     
     
         67 . A method for wireless communications, comprising:
 receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising a first set of frequency domain channel coefficients for an estimated multiple input multiple output (MIMO) channel used to transmit transmissions to the AT and a second set frequency domain channel coefficients for a subset of tones of the estimated channel; and   reconstructing the estimated channel based on the CSI feedback.   
     
     
         68 . An apparatus for wireless communications, comprising:
 logic for receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising a first set of frequency domain channel coefficients for an estimated multiple input multiple output (MIMO) channel used to transmit transmissions to the AT and a second set frequency domain channel coefficients for a subset of tones of the estimated channel; and   logic for reconstructing the estimated channel based on the CSI feedback.   
     
     
         69 . An apparatus for wireless communications, comprising:
 means for receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising a first set of frequency domain channel coefficients for an estimated multiple input multiple output (MIMO) channel used to transmit transmissions to the AT and a second set frequency domain channel coefficients for a subset of tones of the estimated channel; and   means for reconstructing the estimated channel based on the CSI feedback.   
     
     
         70 . A computer-program product for wireless communications, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:
 instructions for receiving channel state information (CSI) feedback from an access terminal (AT), the CSI feedback comprising a first set of frequency domain channel coefficients for an estimated multiple input multiple output (MIMO) channel used to transmit transmissions to the AT and a second set frequency domain channel coefficients for a subset of tones of the estimated channel; and   instructions for reconstructing the estimated channel based on the CSI feedback.